The US is closer to ending prohibition on marijuana than at any time since the Marihuana (sic)Tax Act of 1937, which first made possessing or selling cannabis illegal in the country.

Unlikely bedfellows Rep. Ron Paul (R-TX) and Barney Frank (D-MA) plan to introduce a bill on Thursday that would end the federal prohibition on marijuana.

Theirs are not the only voices calling for marijuana to be legalized.

U.N. Secretary-General Kofi Annan and past presidents of Mexico, Brazil and Colombia have also called for a debate on decriminalisation.

“The U.S. needs to open a debate,” former Colombian President Cesar Gaviria, told media at a Global Commission on Drug Policy event earlier this month. “When you have 40 years of a policy that is not bringing results, you have to ask if it's time to change it.”

Some economists believe that there would be substantial economic benefits to legalizing drugs such as cocaine and heroin.

“There is a strong case for legalizing drugs,” Jeffrey Miron, senior lecturer in economics at Harvard University and a senior fellow at the Cato Institute, told CNBC.com.

“This is based on economic reasoning, but it is broader than just ‘economic effects’,” he said.